Comment by jpxxx | Hacker News Reader

Comment by jpxxx | Hacker News Reader

Not to burst anyone's bubble, but this is not the staggering news it's being made out to be. It is good foundational geology, yes, but water has essentially been confirmed for years now.

The story of Mars in short: flop planet, can't hydrosphere.

There is extremely strong evidence that in the very early years Mars was capable of holding on to a great deal of water: Enough to cover the Southern Hemisphere. The streambed seen here is from that time.

That downer is that this was over 3 billion years ago. Through a variety of processes and for a number of reasons most of Mars' water was lost to space or trapped underground.

The billion-dollar question that would be epic to answer: Did Mars develop Or acquire life during the time it had liquid water on the surface and if so is there any trace of it left, alive or dead?

"... but water has essentially been confirmed for years now. ..."

From the article, "... This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it ..."

Yes, it is good foundational geology being reported upon.

What's cool about that is that it allows you to directly calculate how much water flow was involved in moving this gravel (taking in to account the much lower Martian gravity), you can use the pattern in which the gravel deposited itself to determine what direction the flow was going, and more.

Knowing water was present and knowing what it was doing are two entirely different things.

You do realize that the reason this find is significant is because it gives us more information to answer that last question, right? Especially as we drive our rover over there and study the ever loving crap out of these materials.

Yes, and I do realize I sound like a buzzkill - I was just trying to curb enthusiasm. "Streambed confirmed" conjures ideas of desert playas or dry gullies that are just waiting for rain, when the reality is that we're investigating a planet that hasn't seen liquid precipitation in perhaps billions of years. Condensing out all of the water currently in the Martian atmosphere would produce a layer a few microns thick. It's dry.

"Condensing out all of the water currently in the Martian atmosphere would produce a layer a few microns thick. It's dry."

That's an interesting, and very specific number that I hadn't heard before. Is there a story behind that?

Yawp. Fast factsheet here: http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html

For starters, the remaining atmosphere on Mars is extraordinarily thin. Go to the top of Mt. Everest. Then go four times higher than that. That's the atmospheric pressure at "sea" level on Mars.

It's apparently relatively easy to determine atmospheric composition from afar, and of the atmosphere remaining on Mars, 210 parts per million is water. I have not done the math myself, but I'm assured the total "depth" of water left is measured in microns.

It's really dry. It's really cold. And we'd pop like a balloon stepping outside.

As for how much water is frozen below? SHRUGGGGGG Anyone could make a career answering that. The biggest confounding factor is that the planet is substantially covered in dust, many meters thick in places. It makes remotely sensing what's underneath a real pain in the ass.

The most solid answer so far appears to be "there is a nontrivial amount of ice below the ground". Think "enough to fill the great lakes".

One minor point- the temperature on Mars makes gigantic wide swings. It can get to be pretty warm there. I believe the record high is 81 degrees F, which is what it is this afternoon in Los Angeles. Of course, it also gets down to -200 F, so the swings can be huge.

Temps above freezing have been reported by Curiosity, which is interesting in itself.

I did not know that, thank you! I can only imagine that engineering a rover to withstand those temperature swings is a pain in the ass.

Here's the official site for Curiosity's weather reports.

http://cab.inta-csic.es/rems/marsweather.html

Second minor point: A human stepping out into vacuum does not "pop like a balloon." Death comes quickly but in a more mundane fashion.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.h...

It's still pretty magical to see an actual picture of actual alluvium on the surface.

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